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Posted: April 2, 2008

Nanotechnology brings ancient sarcophagus to life

(Nanowerk News) It was long believed that the statues and relief's of Greek and Roman antiquity were left in their natural state and unpainted, unlike contemporary works from other advanced civilizations like the Egyptians. Archaeologists have known for some time that this popular misconception of Western art was largely a renaissance creation. Classical marble carvings would have been painted originally, although it is rare for any of the polychromy to have survived to the present day. In most cases the colouring has been completely weathered and worn away over the centuries.

Breathing new life into the past

To illustrate this breakthrough in the understanding of ancient art, it was decided to show the world how vibrant these works of art would have looked in their original form. This involved creating reproduction pieces for a special travelling exhibition organized by the Glyptothek museum in Munich, Germany. The project was led by archaeologist Prof. Vinzenz Brinkmann, a leading authority in this field. It represents more than two decades of research on the polychromy of ancient sculpture, undertaken by the leading authorities in museums around the world, in collaboration with scholars from different countries. Paint fragments were analysed using modern techniques such as infrared spectroscopy and recreated with authentic pigments by Prof. Brinkmann and his team. With more than 20 full-size coloured reconstructions of important Greek and Roman works, 'Multicoloured Gods' breaks new ground as the first large-scale effort to recreate the original appearance of ancient sculpture. Starting off in Munich, the exhibition has toured major European cities and is now in the US.

The Alexander Sarcophagus

One of the exhibition's centre pieces is a section of the Alexander Sarcophagus attributed to the 4th Century BC Lydian King Abdalonymos. An ally of Alexander, Abdalonymos had the marble sarcophagus adorned with bas-relief depictions of scenes from the life of his great hero battling against the Persians. This relic, discovered in Lebanon and now housed in the museum of Istanbul, was one of those rare finds containing fragments of original colours, which were painstakingly analyzed and reproduced. It is believed that the Alexander Sarcophagus, was painted by Nicias, a renowned artist of the period who showed Alexander in a vivid red tunic, magenta cape and golden lion-skin headdress.

Preserving and reconstructing with Stereolithography

The first challenge with the sarcophagus was to make a replica section that was precise in every detail. The second challenge was to use a material with hardness and surface qualities similar to marble. A silicone mould could not be used to make an impression due to the danger that the precious paint fragments would be removed by the mold. It was therefore decide to use a scanning technology to generate a three dimensional data set. This was then used to build a more or less consistent 3D-file which could be used for producing the replica by stereolithography (SL), a process that uses photopolymer liquid resins which solidify when exposed to UV laser light. A software program transfers the designer's 3-D CAD model, or in this case a laser scanned file, into an electronic file for SL machines, composing the information into thin cross sections or layers. A laser beam then traces each layer onto the surface of a vat of photopolymer resin, building the part in repeated layers until a solid replica of the original is completed.

Alphaform AG, a German based specialist service bureau was approached by Professor Brinkmann's team to reproduce the part. Alphaform had previously created pieces of art for well known artists like Andrew Barov and the "Bayrische See- und Schlösserverwaltung" - an institution responsible for preserving pieces of art and ancient buildings in the south of Germany. As Alphaform Director Ralf Deuke recalls: "These kind of projects are far removed from our usual rapid prototyping work, for example for automotive and Formula 1 where we receive well designed files with good surfaces."

"The project generated a number of specific challenges: The scan contained a lot of defects due to a combination of the protective glass cover and the space limitations around the original piece in the Istanbul museum. Another big challenge was that the file generated thousands of supports. Some structural supports are necessary while the part is being manufactured using the SL process but not thousands! We therefore had to use our experience and know-how to find a good compromise and produce a file that the machines were able to handle and which showed minimal defects."

NanoTool for precision detailing

To faithfully reproduce the fine detail of the piece also required an SL material with hardness and surface qualities similar to marble. Although Alphaform also use laser sintering techniques [SLS] they decided to use SL because of its superior surface finish and detail resolution. Being thermoplastics, SLS materials can't reproduce mineral-like qualities. The material that could was the SL photopolymer NanoTool® from DSM Somos: a high modulus material designed for high-end engineering applications - in automotive and wind-tunnel testing as well as for rapid tooling. NanoTool is heavily filled with non-crystalline nanoparticles allowing for faster processing. Being a virtually zero shrinkage polymer, build lines don't detract from the smooth finish.

"We have a lot of experience with NanoTool for the rapid prototyping of F1 aero sections and other parts that need high surface quality," continued Deuke, "it provides extremely fine detail resolution compared to other SL materials. Professor Brinkmann evaluated the material and found it easy to finish and paint - far superior to the plaster normally used to create replicas."

"After first creating a small section less than half a meter wide [shown above] we move on to replicating a full three meter side of the sarcopghagus. The complete piece was built in three sections which were then seamlessly fitted together. Without rapid prototyping it would have been impossible to create this part. It's ironic that a material and process designed for next generation prototyping and manufacture has replicated a 2,500 year old sarcophagus!"

About DSM Somos

DSM Somos is one of the world's leading material suppliers to the rapid prototyping industry, providing stereolithography liquids used for the creation of three-dimensional models and prototypes directly from digital data. Somos' patented ProtoFunctional® materials are used by a variety of industries, including automotive, aerospace, medical and telecommunications.

DSM Somos is an unincorporated subsidiary of DSM Desotech-a world leader in the development of UVcurable materials-and a member of the global DSM family.

About Alphaform AG

With wholly owned subsidiary companies in German, Finland and the UK, Alphaform AG has evolved from a Rapid Prototyping service company into a production company of the future. Utilizing the most advanced production techniques, Alphaform customize the development and mass production of parts for a range of end-markets such as automotive, E&E, and medical. Services include rapid prototyping, metal coating, rapid tooling and small scale serial production.